Key Engineering Materials Vols. 330-332

Abstract: The purpose of this study was to evaluate biocompatibility of a new injectable root canal sealer. The cytotoxicity of zinc oxide-eugenol cements, CCQ and the new injectable root canal sealer were assessed by the MTT assays. These materials were filled into the root canals of the dog. One month later, the dog was sacrificed and the X-ray photos were taken. The histological response was observed through the microscope. The results show the new injectable root canal sealer showed better biocompatibility than the other two materials.

Abstract: In this study, the effect of cyanoacrylate-based β-tricalcium phosphate (β-TCP) on pullout strength of orthodontic mini-screw was evaluated. New cements were prepared by mixing Histoacryl® (n-butyl cyanoacrylate) and acid-treated β-tricalcium phosphate. The ratios of β-TCP to Histoacryl® were 0, 0.5, 1.0, and 2.0. Artificial bone blocks were used as a substrate for the miniscrew implantation. The test groups were divided into three groups (one solid bone block [group 1] and a bone block with a 0.9 mm hole [group 2], and a bone block with a 2.5 mm hole [group 3]). And each group was divided into subgroups according to cement usage and non-usage. The used artificial bone density was 0.64g/cm2. Pullout strengths were determined using a universal testing machine. Statistical analysis was performed using the SPSS 9.0 for Windows program. Paired samples t-tests and ANOVA were used with p<0.05. The maximum pullout strengths were 295.9 ± 3.8 N for group 1, 261.1±15.0 N for group 2, and 273.2±20.0 N for group 3. In group 1 and 2, the pullout strength in the subgroup using cement was higher than that of the subgroup of not using cement (p<0.05). In group 3, the pullout strength in the subgroups using cyanoacrylate-based β- TCP cement was higher than that of the subgroup using conventional glass ionomer cement (GC Fuji-I, GC Co., Tokyo, Japan) (p<0.05). These results indicate that our β-TCP/Histoacryl® cements have the potential to enhance pullout strength of the orthodontic mini-screw.

Abstract: The purpose of this study was to evaluate the shear bond strength of composite resin to 4 different all-ceramic coping materials with 3 different surface treatments after thermocycling and without thermocycling. Three different surface treatments - sandblasting with 50 ㎛ alumina particles (AB); sandblasting with 50 ㎛ alumina particles and acid etching with 4% hydrofluoric acid (AE); sandblasting with 50 ㎛ alumina particles and 30 ㎛ alumina particles with tribochemical silica coating (SI) and silane application - were used on four different all-ceramic; Feldspatic ceramic (Duceram Plus); Lithium disilicate ceramic (IPS Empress2); Alumica ceramic (In-Ceram Alumina); Zirconia ceramic (Zi-Ceram) - substrates. Shear bond strength of restorative composite resin to substrate was tested after thermocycling and without thermocycling (n=10). Each specimen was subjected to a shear load at a crosshead speed of 2 ㎜/min until fracture. Two-way analysis of variance and Duncan multiple comparison test (α =0.05) were used to analyze the bond strength values. There were significant differences in the bond strengths for ceramic types (P<.001), surface treatments (P<.001), and thermocycling (P<.001). The Duncan analysis showed that the Si specimens had significantly higher bonding strengths than other specimens. The bond strength of composite resin decreased after thermocycling.

Abstract: The aim of this study was to optimize sintering aids and processing parameters for zirconia toughened alumina (ZTA) nano-ceramics with optimal properties as dental ceramics. Additive agents (TiO2, MgO, SiO2), dry pressing forces and sintering temperatures are very important for preparation of structural ceramics. In the present study, density and Vickers hardness measurement, SEM, and XRD analysis were employed to investigate the effects of these on the final products. The relevant results showed that higher pressing force led to an increase in the density and Vickers hardness of the sintered ceramics. Among the four groups of sintered nanoceramics with different ratios of alumina and zirconia, and combinations of additive agents, the best densification was achieved in the sample from Group 2# containing 1.05wt% MgO after sintered at 1450°C, as indicated by SEM observation. XRD analysis confirmed the formation of MgAl2O4 as an intermediate compound. The existence of TiO2 in the additive agents was in favor of the acquisition of high densification. The measured values for the density and Vickers hardness indicated that the sintered ZTA nano-ceramics would be a potential material for dental prosthetic applications.

Abstract: Precision fit of dental prostheses were compared between the four experimental groups of cast Ni-Cr alloy, cast titanium, milled titanium and milled zirconium by measuring and comparing the mean values of the marginal, axial, occlusal and overall coping-die gaps. The overall, axial and occlusal fit was most precise with the cast Ni-Cr alloy prosthesis. The biologically critical marginal fit was the most precise with the milled zirconium, thus suggesting that the copy-milled zirconia ceramic could serve as an alternative to the cast-metal prosthesis. The statistical variables, such as the groups and the regions, were in association with and had an interaction effect on the adaptability of the prostheses. The marginal gaps correlated with the axial gaps in the cast Ni-Cr alloy and milled titanium groups

Abstract: This study was designed to evaluate mechanical properties and the marginal fitness of glass infiltrated alumina core fabricated from aqueous alumina tape. Utilizing the automatic Dr. Blade model (DP-150 of Japan JinChungjungGi manufacturer) fabricated the slurry into 0.5 ㎜ thickness aqueous-based alumina tape. The coefficient of thermal expansion and biaxial flexural strength of alumina composite produced from alumina tape were investigated. Three upper central resin incisors were prepared with 90o, 110o, 135o shoulder margin for all-ceramic crown. Individual tooth model’s impressions were taken 15times each to make epoxy resin die. Cores were made of alumina tape to each and every dies. Crown setting was done on the epoxy resin dies. The specimens were evaluated for measuring for marginal gaps of glass infiltrated alumina core fabricated from aqueous alumina tapes under 180 magnifications with Kan Scope(Sometech Vision, Korea) was done. The retained measurements were analyzed with Turkey’s Studentized Range Test for marginal fitness of each specimen. Coefficient of thermal expansion of alumina tape was 7.5x10-6/°C, and biaxial flexural strength was observed to be 498±32MPa. The marginal fits of alumina cores made of alumina tapes showed the least marginal gap of 41.5 ㎛ in the 110o shoulder margin, and increasingly with 135o, 90o shoulder margin. Marginal fitness should be better in angles larger than 90o.

Abstract: The aim of this study was to evaluate the remineralizing potential of demineralized human dentin treated with Y/HA nanoparticles (doping Y with 5mol %) and HA nanoparticles suspension and whether dentin could be remineralized by HA. Human crown dentin was demineralized with EDTA for 4 hours, and then subjected to remineralization condition. The ability of these matrices to remineralize was determined by SEM, AFM and calcium levels in the remineralized tissue were measured by atomic energy spectrum analysis. The results showed that Y/HA and HA nanoparticles remineralized the demineralized dentin surface; these demineralized matrices treated with Y/HA nanoparticles remineralized to a greater extent than those treated HA nanoparticles. The differences in both the quality and quantity, as defined by Yttrium iones leading to changes in characterization of the apatite crystals might be important in effecting the ability of this tissue to remineralize. This work suggested that apatite nanoparticles caused remineralization of dentin and the yttrium ions substituted in the apatite structure might enhance their remineralization potential.

Abstract: The purpose of this study is to evaluate the new bone formation of sinus augmentation with using ICB (Irradiated Cancellous Bone & Marrow; Rockey Mountain Tissue Bank, Denver, Co) and MBCP (Micro-Macroporous Biphasic Calcium Phosphate;Biomatlante, France). Study population consisted of 4 patients with maxillary posterior edentulous dentition and ridge heights were less than 5 mm. ICB (Rockey Mountain Tissue Bank, Denver, Co) and MBCP (Biomatlante, France) is mixed with 50: 50. After 6 months, the bone biopsies were done with 2mm trephine bur from lateral window opening. Mean new bone formations were 26.84 %, the residual grafts were 4.92 and soft tissues were 67.98 %. The small number of biopsies did not permit analysis of statistical significance. The variability of individual patient factors do not permit definitive conclusions. The mixtures of ICB & MBCP were superior or comparable to another various bone alternative materials in new bone formation of sinus floor elevation.

Abstract: Sensory perception thresholds of implants were much higher than those of natural teeth. The purpose of this study was to evaluate the biocompatibility of TiO2/HA-biocoated dental implants for nerve regeneration using cultured Schwann cells. The nano-TiO2/HA composite bioceramic coating was developed on the surfaces of commercially pure titanium discs by sol-gel route, and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Using smooth titanium discs as a control, Schwann cell responses to the coating were evaluated by SEM, MTT assay, total protein content and leakage of cytosolic lactate dehydrogenase (LDH) activity. In addition, the amount of brain-derived neurotrophic factor (BDNF) secreted by Schwann cells was measured by Enzyme-Linked Immunosorbent Assay (ELISA). It was observed that the coating had fine crystallites and homogeneous micropores in the diameter of 5-10 um. The cell morphology, proliferation and function were unaffected. The results indicate that the TiO2/HA bioceramic coating developed on the surface of pure titanium by sol-gel route had good biocompatibility with Schwann cells for nerve regeneration around dental implants.